Contact lenses are thin, curved lenses that are placed directly on the surface of the eye (the cornea) to correct vision, similar to eyeglasses. They can correct common refractive errors like nearsightedness, farsightedness, and astigmatism by adding or subtracting focusing power to the eye. Contact lenses can also be used for cosmetic purposes, to change eye color, or to treat certain eye conditions. They come in different materials, such as soft lenses and rigid gas permeable (RGP) lenses, and vary in wear schedules, from daily disposables to extended-wear lenses